The present invention relates to a polymerization process for the preparation of ethylene polymers in the presence of a metallocene catalyst. The invention also relates to a process for the preparation of the relevant metallocenes and of the corresponding ligands, which are useful as intermediates in the synthesis of said metallocene compounds. The invention further relates to ethylene copolymers obtainable with those metallocene catalysts.
Metallocene compounds having two bridged cyclopentadienyl or indenyl groups are known as catalyst components for the home and copolymerization reaction of ethylene.
Also known are metallocene compounds containing a bridged bis-fluorenyl ligand system for use in the polymerization of olefins.
For instance, in EP-A-0 632 066 it is discloses the use of bis-fluorenyl based metallocenes for the production of elastomeric copolymers of ethylene with propylene.
More recently, heterocyclic metallocene compounds used in the polymerization of alpha-olefins have been disclosed.
For example, PCT application WO 98/22486 discloses metallocenes containing a cyclopentadienyl radical directly coordinating the central metal atom, to which are fused one or more rings containing at least one heteroatom. These metallocenes, in combination with a suitable cocatalyst, are used in the polymerization of olefins such as ethylene. However, the molecular weight that can be obtained is still not sufficient for many uses and the activity of the catalyst systems containing said metallocenes, when used in the polymerization of ethylene, is not satisfactory.
It would be desirable to identify metallocene catalysts capable of yielding ethylene polymers having a high molecular weight and which also have high activities, such that the amount of the catalyst remaining in the polymer is minimized. Further, it would be advantageous to obtain copolymers of ethylene with alpha-olefins and polyenes in which the comonomer units in the polymeric chain are homogeneously distributed.
It has been found unexpectedly that it is possible to achieve the above and other results by carrying out the polymerization reaction of ethylene in the presence of a catalyst based on a class of heteroatom containing metallocene compounds.
Thus, according to a first aspect of the present invention a process is provided for the preparation ethylene polymers, comprising the polymerization reaction of ethylene and optionally one or more olefins in the presence of a catalyst comprising the product obtainable by contacting:
(A) a metallocene compound of the general formula (1):
SiR1R2LQMXpxe2x80x83xe2x80x83(I) 
wherein SiR1R2 is a divalent group bridging the moieties L and Q;
R1 and R2, which may be the same or different, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; optionally R1 and R2 form a ring comprising from 3 to 8 atoms, which can bear substituents;
Q is a moiety of formula (II): 
wherein A and B are selected from sulfur (S), oxygen (O) and CR5, R5 is selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; and wherein the rings containing A and B have a double bond in the allowed position having an aromatic character, either A or B being different from CR5 i.e. if A is S or O, B is CR5 or if B is S or O, A is CR5;
R3 and R4, which may be the same or different , are selected from hydrogen a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; preferably R3 and R4, which may be the same or different, are selected from a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; L is a moiety of formula (III): 
wherein R6, R7, R8 and R9, which may be the same or different, are selected from C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; and two adjacent R6 and R7 and/or R8 and R9 can form a ring comprising from 3 to 8 atoms, which can include heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements and can bear substituents;
M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version), X, which may be the same or different, is a ligand selected from hydrogen, halogen, R10, OR10, OSO2CF3, OCOR10, SR10, NR102 or PR102 group, wherein R10 is selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
p is an integer of from 0 to 3, preferably from 1 to 3 being equal to the oxidation state of the metal M minus 2 and
(B) an alumoxane and/or a compound capable of forming an alkyl metallocene cation. The transition metal M is preferably selected from titanium, zirconium and hafnium preferably in the formal oxidation state of +4. Most preferably zirconium is used. Preferably p is 2.
The X substituents are preferably chloride or methyl groups.
Preferably the substituents R1 and R2 are C1-C20-alkyl groups such as methyl group; R3 and R4 are C1-C20-alkyl groups optionally containing silicon atoms or C6-C20-aryl groups, such as methyl, tert-butyl, phenyl, trimethylsilyl groups; R6, R7, R8 and R9 are C1-C20-alkyl groups such as methyl, tert-butyl, A is sulfur and B is CH.
A further object of the present invention is a metallocene compound of formula (1)
SiR1R2LQMXpxe2x80x83xe2x80x83(I) 
Wherein R1, R2, L, Q, M, X and p are described above.
Non-limiting examples of metallocene compounds suitable for use in the process of the invention are: dimethylsilandiyl-(tetramethylcyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-(tetraethylcyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-(tetraethylcyclopentadienyl)-7-(2.5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-diethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-diisopropyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-ditertbutyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(cyclopentadienyl-1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-ditrimethylsilyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(tetramethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-diethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(tetramethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-diisopropyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(tetramethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-diisopropyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(tetramethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-7-(3-trimethylsilylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-zirconium dichloride and dimethyl, dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-9-(fluorenyl)-zirconium dichloride and dimethyl, b:3,4-bxe2x80x2]-dithiophene) zirconium dichloride and dimethyl.
xe2x80x9cParticularly interesting metallocenes of formula (I) for use in the process of the invention are those in which L is a moiety of formula (IV): 
wherein R14, R11, R12 and R13, which may be the same or different, are selected from hydrogen, a C1-C20-alkyl, C3-C2-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, and optionally two adjacent R14, R11, R12 and R13 groups can form a ring having 3 to 8 atoms, which can bear substituents.
Preferably R14, R12 and R13 are hydrogen and R11 are selected from hydrogen and a C1-C20-alkyl groupxe2x80x9d.
Most preferably R11 is selected from hydrogen and a tert-butyl radical.
Non-limiting examples belonging to this class are:
dimethylsilandiyl-7-(2,5dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-9-(fluorenyl)-zirconium dichloride and dimethyl,
dimethylsilandiyl-7-(2,5-diethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-9-(fluorenyl)-zirconium dichloride and dimethyl,
dimethylsilandiyl-7-(2,5-diisopropyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-9-(fluorenyl)-zirconium dichloride and dimethyl,
dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)-9-(2,7-dimethylfluorenyl)-zirconium dichloride and dimethyl,
dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)9-(2,7-diethylfluorenyl)-zirconium dichloride and dimethyl,
dimethylsilandiyl-7-(2,5-dimethyly-clopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)9-(2,7-diisopropylfluorenyl)-zirconium dichloride and dimethyl.
dimethylsilandiyl-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene9-(2,7-ditertbutylfluorenyl)-zirconium dichloride and dimethyl.
Other interesting metallocenes of formula (I) for use in the process of the invention are those in which L is a moiety of formula (IIxe2x80x2): 
wherein A and B are defined as above, R3, and R4,, which may be the same or different, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
Preferred compounds are those, in which A is sulfur and B is a CH group, R3xe2x80x2 and R4xe2x80x2 are selected from a C1-C20-alkyl group.
Most preferably R3xe2x80x2 and R4xe2x80x2 are methyl groups.
Non-limiting examples belonging to this class are:
dimethylsilandiylbis-7-(2,5-dimethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl,
dimethylsilandiylbis-7-(2,5diethyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl,
dimethylsilandiylbis-7-(2,5-diisopropyl-cyclopentadienyl-[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl,
dimethylsilandiylbis-7(2,5-diterbutyl-cyclopentadenyl[1,2-b:4,3-bxe2x80x2]-dithiophene)zirconium dichloride and dimethyl.
The alumoxane used as component (B) can be obtained by reacting water with an organo-aluminium compound of formula HjAlR153j or HjAl2R156j, where the R15 substituents, which may be the same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cyclalkyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-aryalkyl, optionally containing silicon or germanium atoms with the proviso that at least one R15 is different from halogen, and J ranges from 0 to 1, being also a non-integer number. In this reaction the molar ratio of Al/water is preferably comprised between 1:1 and 100:1.
The molar ratio between aluminium and the metal of the metallocene is comprised between about 10:1 and about 20000:1, and more preferably between about 100:1 and about 5000:1. The alumoxanes used in the catalyst according to the invention are considered to be linear, branched or cyclic compounds containing at least one group of the type: 
wherein the R15 substituents, which may be the same or different, are described above. In particular, alumoxanes of the formula: 
can be used in the case of linear compounds, wherein n is 0 or an integer from 1 to 40 and the R15 substituents are defined as above, or alumoxanes of the formula: 
can be used in the case of cyclic compounds, wherein n is an integer from 2 to 40 and the R15 substituents are defined as above.
Examples of alumoxanes suitable for use according to the present invention are methylalumoxane (MAO), tetra-isobutyl)alumoxane (TIBAO), tetra-(2,4,4trimethyl-pentyl)alumoxane (TIOAO), tetra-(2,3-dimethylbutyl)alumoxane (TDMBAO) and tetra-(2,3,3-trimethylbutyl)alumoxane (TTMBAO).
Particularly interesting cocatalysts are those disclosed in WO 99/21899 and in PCT/EP00/09111 in which the alkyl and aryl groups have specific branched patterns.
Non-limiting examples of aluminium compounds according to said PCT applications are: tris(2,3,3-trimethyl-butyl)aluminium, tris(2,3dimethyl-hexyl)aluminium, tris(2,3dimethyl-butyl)aluminium, tris(2,3-dimethyl-pentyl)aluminium, tris(2,3-dimethyl-heptyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminium, tris(2-methyl-3-ethyl-hexyl)aluminium, tris(2-methyl-3-ethyl-heptyl)aluminium, tris(2-methyl-3-propyl-hexyl)aluminium, tris(2-ethyl-3-methyl-butyl)aluminium, tris(2-ethyl-3-methyl-pentyl)aluminium, tris(2,3diethyl-pentyl)aluminium, tris(2-propyl-3-methyl-butyl)aluminium, tris(2-isopropyl-3-methyl-butyl)aluminium, tis(2-isobutyl-3-methyl-pentyl)aluminium, tris(2,3,3-trimethyl-pentyl)aluminium, tris(2,3,3-trimethyl-hexyl)aluminium, tris(2ethyl-3,3-dimethyl-butyl)aluminium, tris(2-ethyl-3,3-dimethyl-pentyl)aluminium, tris(2-isopropyl-3,3-dimethyl-butyl)aluminium, tris(2-trimethylsilyl-propyl)aluminium, tris(2-methyl-3-phenyl-butyl)aluminium, tris(2-ethyl-3-phenyl-butyl)aluminium, tris(2,3-dimethyl-3-phenyl-butyl)aluminium, tris(2-phenyl-propyl)aluminium, tris[2-(4-fluoro-phenyl)propyl]aluminium, tris[2(4-chloro-phenyl)-propyl]aluminium, tris[2-(3-isopropyl-phenyl)-propyl]aluminium, tris(2-phenyl-butyl)aluminium, tris(3-methyl-2-phenyl-butyl)aluminium, tris(2-phenyl-pentyl)aluminium, tris[2-(pentafluorophenyl)-propyl]aluminium, tris[2,2-diphenyl-ethyl]aluminium and tris[2-phenyl-2-methyl-propyl]aluminium, as well as the corresponding compounds wherein one of the hydrocarbyl groups is replaced by an hydrogen atom, and those wherein one or two of the hydrocarbyl groups are replaced by an isobutyl group.
Amongst the above aluminium compounds, trimethylaluminium (TMA), triisobutylaluminium (TIBAL), tris(2,4,4trimethyl-pentyl)aluminium (TIOA), tris(2,3dimethylbutyl)aluminium (TDMBA) and tris(2,3,3-trimethylbutyl)aluminium (TTMBA) are preferred.
The molar ratio between the aluminium and the metal of the metallocene compound is in general comprised between 10:1 and 20000:1, and preferably between 100:1 and 5000:1.
Non-limiting examples of compounds able to form an allylmetallocene cation are compounds of formula D+Exe2x88x92, wherein D+ is a Brxc3x8nsted acid, able to give a proton and to react irreversibly with a substituent X of the metallocene of formula (I) and Exe2x88x92 is a compatible anion, which is able to stabilize the active catalytic species originating from the reaction of the two compounds, and which is sufficiently labile to be able to be removed by an olefinic monomer. Preferably, the anion Exe2x88x92 consists of one or more boron atoms. More preferably, the anion Exe2x88x92 is an anion of the formula BAr4(xe2x88x92), wherein the substituents Ar which can be identical or different are aryl radicals such as phenyl, pentafluorophenyl or bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly preferred. Moreover, compounds of the formula BAr3 can conveniently be used. Compounds of this type are described, for example, in the published International patent application WO 92/00333, the content of which is incorporated in the present description.
The catalysts of the present invention can also be used on supports. This is achieved by depositing the metallocene compound (A) or the product of the reaction thereof with the component (B), or the component (B) and then the metallocene compound (A) on supports such as, for example, silica, alumina, magnesium halides, styrene/divinylbenzene copolymers, polyethylene or polypropylene.
A suitable class of supports, which can be used, is constituted by porous organic supports functionalized with groups having active hydrogen atoms. Particularly suitable are those in which the organic support is a partially crosslinked styrene polymer. Supports of this type are disclosed in European application EP-A0 633 272.
Another class of inert supports particularly suitable for use according to the invention is that of the olefin, particularly propylene, porous prepolymers described in International application WO 95/26369.
A further suitable class of inert supports for use according to the invention is that of the porous magnesium halides such as those described in International application WO 95/32995.
The solid compound thus obtained, in combination with the further addition of the alkylaluminium compound either as such or prereacted with water if necessary, can be usefully employed in the gas-phase polymerization.
The process for the polymerization of olefins according to the invention can be carried out in the liquid phase in the presence or absence of an inert hydrocarbon solvent, or in the gas phase. The hydrocarbon solvent can be either aromatic such as toluene, or aliphatic such as propane, hexane, heptane, isobutane or cyclohexane.
The polymerization temperature is generally comprised between xe2x88x92100xc2x0 C. and +200xc2x0 C. and, particularly between 10xc2x0 C. and +90xc2x0 C. The polymerization pressure is generally comprised between 0,5 and 100 bar.
The lower the polymerization temperature, the higher are the resulting molecular weights of the polymers obtained.
The polymerization yields depend on the purity of the metallocene compound of the catalyst The metallocene compounds obtained by the process of the invention can therefore be used as such or can be subjected to purification treatments.
The components of the catalyst can be brought into contact with each other before the polymerization. The pre-contact concentrations are generally between 1 and 10xe2x88x928 mol/l for the metallocene component (A), while they are generally between 10 and 10xe2x88x928 mol/l for the component (B). The pre-contact is generally effected in the presence of a hydrocarbon solvent and, if appropriate, of small quantities of monomer.
According to another aspect of the present invention a process is provided for the preparation of a ligand of formula (V):
SiR1R2Qxe2x80x2Lxe2x80x2xe2x80x83xe2x80x83(V) 
wherein
Qxe2x80x2 is a moiety of the general formula (VI): 
and its double bond isomers, wherein A, B, R3 and R4 are defined as described above; Lxe2x80x2 is a moiety of the general formula (VII): 
and its double bond isomers, wherein R1, R2 R6, R7, R8 and R9 are defined as described above above, comprising the following steps:
i) treating the compound of formula (VIII) with at least one equivalent of a base selected from the group consisting of metallic sodium and potassium, sodium and potassium hydroxide and an organolithium compound; 
xe2x80x83wherein the rings containing A and B have a double bond in the allowed position having an aromatic character, A, B, R3 and R4 are defined as above;
ii) contacting the corresponding anionic compound obtained under i) with a compound of general formula (IX):
YLxe2x80x2SiR1R2xe2x80x83xe2x80x83(IX) 
wherein Lxe2x80x2, R1, R2 have the meaning described above and Y is a halogen atom selected from the group consisting of fluoride, chloride, bromide and iodide;
An alternative process for preparing the ligand of formula (V) comprises the following steps:
i) treating the compound of formula (VIII) with at least one equivalent of a base selected from the group consisting of metallic sodium and potassium, sodium and potassium hydroxide and an organolithium compound; 
xe2x80x83wherein the rings containing A and B have a double bond in the allowed position having an aromatic character, A, B, R3 and R4 are defined as above;
ii) contacting the corresponding anionic compound obtained under i) with a compound of general formula (X):
Y2SiR1R2xe2x80x83xe2x80x83(X) 
wherein Lxe2x80x2, R1, R2 have the meaning described above and Y is a halogen atom selected from the group consisting of fluoride, chloride, bromide and iodide;
iii) contacting the product obtained in step ii) with a compound of formula (XI) 
wherein R6, R7, R8 and R9 are described above and G is selected from sodium, potassium and lithium, preferably G is lithium.
The synthesis of the above bridged ligand is preferably carried out by adding a solution of an organolithium compound in an apolar solvent to a solution containing the compounds of formulae (VII) and (IX) respectively in an aprotic polar solvent. The bridged ligand can be separated by conventional general known procedures.
Not limitating examples of aprotic polar solvents which can be used in the above process are tetrahydrofurane, dimethoxyethane, diethylether, toluene and dichlorometane. Not limiting examples of apolar solvents suitable for the above process are pentane, hexane and benzene. During the whole process, the temperature is preferably kept between xe2x88x9280xc2x0 C. and 100xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
The compound of formula (VII) is an important intermediate for preparing the ligand of formula (V). When both R3 and R4 are hydrogen the corresponding compound of formula (VII) is obtained according to WO 98/2486.
In the case that B is a CR5 group and preferably R4 and R5 the which may be the same or different from each other, are selected from a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, the corresponding compound of formula (VII) can be obtained with a process comprising the following steps:
i) treating a compound of formula (XII): 
xe2x80x83wherein A is sulfur or oxygen, with a compound of formula (XIII): 
xe2x80x83wherein A is sulfur or oxygen,
ii) contacting the thus obtained product with a reducing agent in a molar ratio between said reducing agent and the product obtained under i) of at least 1;
iii) contacting the product obtained under ii) with a compound selected from an organotithium compound, sodium and potassium in a molar ratio between said compound and the product obtained in step ii) of equal to or greater than 2;
iv) treating the thus obtained product with an agent selected from the group consisting of copper chloride, iodine and Mg/Pd., in order to obtain a compound of general formula (XIV): 
When B is sulfur or oxygen and A is a CR5 group and preferably R4 and R3 the which may be the same or different from each other, are selected from a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, the corresponding compound of formula (VI) can be obtained according to the process comprising the following steps:
i) contacting a compound of formula (XV): 
xe2x80x83wherein B is sulfur or oxygen, with a compound of formula (XVI): 
xe2x80x83wherein B is sulfur or oxygen, and subsequently treating with a neutralization agent;
ii) treating the thus obtained product with a reducing agent in a molar ratio between said reducing agent and the compound obtained under i) of at least 1;
iii) contacting the thus obtained product with a mixture of an organolithium compound and tetramethylethylenediamine (TMEDA) in a molar ratio between said mixture and the product obtained under ii) of at least 2,
iv) contacting the thus obtained product with an agent selected from the group consisting of copper chloride, iodine and Mg/Pd, in order to obtain a compound of formula (XVII): 
An alternative process for preparing the compound of formula (VII) when A is S or O and preferably R4 and R3 the which may be the same or different from each other, are selected from a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, comprises the following steps:
i) contacting an equimolar mixture of compounds of formulae (XVIII) and (XIX): 
xe2x80x83wherein A are sulfur or oxygen, with a Lewis acid or a mixture of a Lewis acid and a protonic acid;
ii) treating the thus obtained product with CH2O in a molar ratio between said mixture and CH2O of a range between 10:1 and 1:10;
iii) contacting the thus obtained product with a compound selected from an organolithium compound, sodium and potassium;
iv) contacting the thus obtained product with an agent selected from the group consisting of copper chloride, iodine and Mg(Pd., in order to obtain a compound of general formula (XIV)
The Lewis acid used in the above processes is preferably selected from zinc dichloride, cadmium dichloride, mercurium dichloride, tin tetrachloride, trifluoroborane, zirconium tetrachloride, titanium tetrachloride. Most preferably, the Lewis acid is zinc dichloride. In the above processes the agent used is preferably copper chloride; preferably the reducing agent is a mixture of AlCl3/LiAlH4; the organolithium compound used above is preferably butyllithium.
Compounds of formula (VII) can suitable be used as intermediates for the preparation of metallocenes of formula (I)
Thus, it is a further aspect of the present invention a process for the preparation of a metallocene of the general formula (I):
SiR1R2QLMXpxe2x80x83xe2x80x83(I) 
wherein Q, L, R1, R2, M, X and p have the meaning as defined above, comprising the following steps:
a) contacting a compound of the formula (VI):
SiR1R2Qxe2x80x2Lxe2x80x2xe2x80x83xe2x80x83(VI) 
xe2x80x83wherein
Qxe2x80x2, xe2x80x2L, R1 and R2 are defined as mentioned above with a base, wherein the ratio between said base and the compound of formula (VI) is at least 2,
b) contacting the obtained product with a compound of formula MXp+Z, wherein M and X are defined as stated above and p is an integer equal to the oxidation state of the metal minus 2.
Preferably, the base is buthyllithium.
Preferably MXp+2 is selected from ZrCl4, TiCl4, HfCl4 and the C1-C6-alkyl analogues thereof. The reaction is carried out in an inert solvent such as toluene, tetrahydrofurane, benzene, diethyl ether, hexane and the like at a temperature range from xe2x88x9278xc2x0 C. to 100xc2x0 C.
In the case in which at least one substituent X in the metallocene compound of the formula (I) is different from halogen an alternative process for preparing it, consists in preparing the dihalogen derivative i.e. the complex wherein both X are halogen and then substituting the halogen atom with the appropriate X group by means of generally applied methods. For example, if the desired substituents X are alkyl groups, the metallocenes can be made to react with alkylmagnesium halides (Grignard reagents) or with alkyllithium compounds. General methods for substituting X by substituents other than halogen such as sulfur, phosphorus, oxygen, etc. are described in Chem. Rev. 1994, 94, 1661-1717, and the therein cited references.
In the process according to the present invention ethylene homopolymers are obtainable having a remarkably high molecular weight. In fact, with the process of the present invention it is possible to obtain ethylene polymers having intrinsic viscosity values (I.V.) as high as 5.0 dl/g and even higher.
In the copolymers obtainable with the process of the invention, the molar content of ethylene derived units is generally higher than 40%, and preferably it is comprised between 50% and 99%, and most preferably it is comprised between 80% and 98%.
The molar content of alpha-olefin derived units is preferably comprised between 0% and 60% and, more preferably, between 1% and 50%, and most preferably between 2% and 20%.
Non-limiting examples of alpha-olefins which can be used as alpha-olefins in the process of the invention are propylene, 1-butene, 1-pentene, 4methyl-1-pentene, 1-hexene, 1-octene, 4,6-dimethyl-1-heptene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and allylcyclohexane.
Non-limiting examples of cycloolefins that can be used as comonomers in the process of the present invention are cyclopentene, cyclohexene and norbornene.
The copolymers according to the invention can also contain units derived from polyenes. The content of polyene derived units, if any, is preferably comprised between 0% and 30% by mol and, more preferably between 0 mol % and 20 mol %.
The polyenes that can be used as comonomers in the copolymers according to the present invention are included in the following classes:
non-conjugated diolefins able to cyclopolymerize such as, for example, 1,5-hexadiene, 1-6-heptadiene, 2-methyl-1,5-hexadiene;
dienes capable of giving unsaturated monomeric units, in particular conjugated dienes such as, for example, butadiene and isoprene, and linear non-conjugated dienes, such as, for example, trans 1,4-hexadiene, cis 1,4-hexadiene, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene, and cyclic non-conjugated dienes such as 5-ethylidene-2-norbornene
The analysis of the distribution of the comonomer units in the copolymers of the invention has been carried out by means of 13C-NMR spectroscopy. The assignments were carried out as described by Randall in Macromol.Chem.Phys. 29, 201, 1989. The distribution of triads, in the case of ethylene/1-hexene, are calculated by means of the following relationships:
HHM=Txcex2xcex2EHE=Txcex4xcex4HHE=Txcex2xcex4HEH=Sxcex2xcex2HEE=Sxcex2xcex4EEE=0.5(Sxcex4xcex4+0.5Sxcex3xcex4) 
wherein EHE, HHE and HHH represent the sequence ethylene/1-hexene/ethylene, 1-hexene/1-hexene/ethylene and 1-hexene/1-hexene/1-hexene respectively in the copolymer. For the NMR nomenclature, see J. Carman, R. A. Harrington, C. E. Wilkes, Macromolecules, 10, 537 (1977). The sum of the triads is normalized to 100. The higher the number of isolated 1-hexene units in the polymeric chain, the more the values of the ratio EHE/(EHE+HHE+HHH) become closer to the unit.
The number of 1-hexene sequences is generally a function of the amount of 1-hexene units present in the chain.
The Tables 2 and 3 refer to ethylene/1-hexene copolymers obtained with a process according to the present invention.
In particular, in Table 3 there are reported the ratios EHE/(EHE+HHE+HHH) as a function of the molar percentage of 1-hexene in the chain for ethylene/1-hexene copolymers obtained with a process according to the present invention, in the presence of the metallocene compounds reported above.
In the case of ethylene/1-hexene, the reactivity ratio r1 and the product of the reactivity ratios r1.r2 are calculated according to the following formulae as described in J. Uozomi, K. Soga, Mak. Chemie, 193, 823, (1992):
r1=2[EE]/[EH]X
r1.r2=4[EE][HH]/[EH]2 
wherein X=[E]/[H] monomer molar ratio in the polymerization bath.
The process of the present invention can also be carried out in a gas phase for the polymerization of ethylene with alpha-olefins such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 4,6-dimethyl-1-heptene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and allylcyclohexane.
Particularly good results are obtained in the gas phase when the polymerization of ethylene is carried out with 1-octene.
The process of the present invention can be also used as last step of a multistep process described in EP 720629 and EP 742801. In this process a polymer previously prepared with a different catalyst system is impregnated with the olefin polymerization catalyst system herein and then ethylene and one or more olefins are polymerized according to the process of the present invention. The polymer of the first steps range from 10 to 70% of the total polymer obtained in the multistep process, preferably from from 10 to 60%, more preferably 20 to 50%.
The metallocene compounds of the general formula (I) as defined above are particularly useful for the preparation of copolymer of ethylene with propylene and optionally a polyene. Therefore, according to another aspect the present invention relates to a copolymer of ethylene with propylene and a polyene, having a content of ethylene derived units comprised between about 35 mol % and 85 mol %, a content of C4-C10-alpha-olefin derived units comprised between about 10 mol % and 60 mol % and a content of a C4-C30-polyene derived units comprised between about 0.1 mol % and 5 mol %, and having the following characteristics:
(A) the % by mole content of the xcex1-olefin in the copolymer (%xcex1) and the ratio Excex1E/(Excex1E+xcex1xcex1E+xcex1xcex1xcex1), wherein Excex1E, xcex1xcex1E and xcex1xcex1xcex1 represent the sequences ethylene/xcex1-olefin/ethylene, xcex1-olefin/xcex1-olefin/ethylene and xcex1-olefin/xcex1-olefin/xcex1-olefin respectively in the copolymer, satisfy the following relationship: 0.01% xcex1+Excex1E/(Excex1E+xcex1xcex1E+xcex1xcex1xcex1)xe2x89xa71
(B) less than 2% of the CH2 groups in the polymeric chain are sequences (CH2)n, wherein n is an even number.
The molar content of the ethylene derived units is preferably comprised between about 50% and 85% and, more preferably, between about 60% and 80%.
The molar content of the xcex1-olefin derived units is preferably comprised between about 15% and 50% and, more preferably, between about 20% and 40%.
The molar content of the polyene derived units is preferably comprised between about 0.1% and 4% and, more preferably, between about 0.1% and 3%.
The polyenes that can be used as comonomers in the copolymers according to the present invention are comprised in the following classes:
non-conjugated diolefins able to cyclopolymerize such as, for example, 1,5-hexadiene, 1-6-heptadiene, 2-methyl-1,5-hexadiene;
dienes capable of giving unsaturated monomeric units, in particular conjugated dienes such as, for example, butadiene and isoprene, and linear non-conjugated dienes, such as, for example, trans 1,4-hexadiene, cis 1,4-hexadiene, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene, and cyclic non-conjugated dienes such as 5-ethylidene-2-norbornene
A preferred polyene for use in the copolymers of the invention is 5-ethylidene-2-norbornene (ENB).
Non-limiting examples of cycloolefins that can be used as comonomers in the process of the invention are cyclopentene, cyclohexene and norbornene.
The copolymers according to the invention can also contain units derived from polyenes. The content of polyene derived units, if any, is preferably comprised between 0% and 4% and, more preferably between 0% and 3%.
In the case of polyenes other than non-conjugated alpha-omega-diolefins having 6 or more carbon atoms, these are preferably used in quantities of between 0 and 3 mol % as a second alpha-olefin comonomer.
A particular interesting embodiment of the present invention is constituted of copolymers of ethylene with propylene, 1-hexene or higher alpha-olefins.
The analysis of the distribution of the comonomer units in the copolymers of the invention has been carried out by means of 13C-NMR spectroscopy. The assignments were carried out as described by M. Kagugo et al. in xe2x80x9cMacromolecules, 15, 1150-1152 (1982)xe2x80x9d. The distribution of triads, in the case of ethylene/propylene, are calculated by the following relationship:
EPE=Txcex4xcex4PPE=Txcex2xcex4PPP=Txcex2xcex2PEE=Sxcex1xcex4PEP=Sxcex2xcex2EEE=0.5(Sxcex4xcex4+0.5Sxcex3xcex4) 
wherein EPE, PPE, PPP, PEE, PEP and EEE represent the sequences ethylene/propylene/ethylene, propylene/propylene/ethylene, propylene/propylene/propylene, propylene/ethylene/ethylene, propylene/ethylene/propylene and ethylene/ethylene/ethylene respectively in the copolymer. The sum of the triads is normalized to 100. In the case of terpolymers the molar composition is calculated from 1H-NMR spectra. EPE, PPE, PPP, PEE, PEP and EEE triads are calculated from 13C-NMR spectra as previously described for the copolymers, neglecting the presence of the termonomer. The higher the number of isolated propylenic units in the polymeric chain, the more the values of the ratio EPE/(EPE+PPE+PPP) become closer to the unity. Generally it is a function of the amount of propylenic units present in the chain.
The Tables 4 and 5 refer to ethylene/propylene copolymers obtained with a process according to the present invention.
In particular, the percentage molar content of propylene in the copolymer of the present invention (%P) and the ratio EPE/(EPE+PPE+PPP) satisfy the following relationship:
0.01%P+EPE/(EPE+PPE+PPP)xe2x89xa71 
preferably:
0.0080%P+EPE/(EPE+PPE+PPP)xe2x89xa71 
more preferably
0.006%P+EPE/(EPE+PPE+PPP)xe2x89xa71. 
In particular, in Table 5 there are reported the ratios EPE/(EPE+PPE+PPP) as a function of the molar percentage of propylene in the chain for ethylene/propylene copolymers obtained with a process according to the present invention, in the presence of the metallocene compounds reported above.
In the copolymers obtained with a process according to the present invention, the product of the reactivity ratios r1.r2, wherein r1 is the reactivity ratio of propylene and r2 that of ethylene, calculated according to the following formula:
r1r2=1+f("khgr"+1)-(f+1)("khgr"+1)xc2xd
wherein
f=ratio between moles of ethylene units and moles of propylene units in the copolymer, and "khgr"=(PPP+PPE)/EPE,
appears to be extremely low. In particular, it is generally lower than 0.2, preferably lower than 0.1 and, more preferably, lower than 0.08.
The propylene units in the copolymer obtained according to the present invention appear to be highly regioregular. In fact, from the 13C-NMR analysis no signals are revealed as deriving from the (CH2)n sequence where n is an even number. Preferably, less than 1% of the CH2 groups in the chain are contained in a (CH2)n sequence, where n is an even number.
The copolymers of the present invention have intrinsic viscosity values (I.V.) generally higher than 0.5 dl/g and preferably higher than 1.0 dl/g. The intrinsic viscosity can reach values of 4.0 dl/g and even higher.
The molecular weight of the polymers can also be modified by varying the type or the concentration of the catalyst components, or by using molecular weight regulators such as, for example, hydrogen.
Generally, the polymers of the present invention are endowed with a narrow molecular weight distribution. The molecular weight distribution is represented by the ratio Mw/Mn which, for the polymers of the present invention, when the metallocene used is a pure isomer, is generally lower than 4, preferably lower than 3.5 and, more preferably, lower than 3.
The molecular weight distribution can be varied by using mixtures of different metallocene compounds or by carrying out the polymerization in several stages at different polymerization temperatures and/or different concentrations of the molecular weight regulators.
The polymers of the invention are generally soluble in common solvents, such as, for instance, chloroform, hexane, heptane, toluene and xylene.
Another object of the present invention is an elastomeric copolymer obtainable by subjecting a copolymer according to the present invention to a vulcanization process.
The copolymers of the present invention may be vulcanized using the known techniques and methods for the EPR and EPDM rubbers, operating, for example, in the presence of peroxides or sulfur. Rubbers are obtained having valuable elastomeric properties.
Still another object of the present invention is a shaped article obtained from the above said elastomeric copolymer.
The rubbers obtained from the copolymers of the present invention are transformable into shaped articles by the normal thermoplastic material processing, such as molding, extrusion, injection, etc. The relative shaped articles are endowed with interesting elastomeric properties and find uses in all typical applications of the ethylene-based elastomers, such as EPR and EPDM.
In particular, the products obtained from the copolymers of the present invention which have a high content of ethylene units, can be advantageously used as coatings for wires and cables. The following examples are given for illustrative purposes and are not intended to limit the scope and spirit of the invention.